Add bundler 1.15.1, remove bundler 1.15.0
Add bundler 1.15.1, remove bundler 1.15.0

source url: https://rubygems.org/downloads/bundler-1.15.1.gem
source sha256: fa6ec48f94faffe4987f89b4b85409fd6a4ddce8d46f779acdc26d041eb200d7

[#146502569]

cloudfoundry/ruby-buildpack,ekaranto/rails4-bluemix-buildpack,cloudfoundry/ruby-buildpack,ekaranto/rails4-bluemix-buildpack,ekaranto/rails4-bluemix-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,ekaranto/rails4-bluemix-buildpack,cloudfoundry/ruby-buildpack